Relay system



g- 1, 1950 E. LABIN ETAL 2,516,885

RELAY SYSTEM Filed April 17,1944 6 Sheets-Sheet 1 Y a; INVEN TORS EM/Lf mB/N DO/YHLD 0. 69/50 ATTORNEY Aug. 1, 1950 Filed April 17, 1944 CHEW/ER PULSE-5 6a VIDEO PULSES oesLom/va Pumas 5 561. 56750 arm/MEL 66 E. LABIN ETAL RELAY SYSTEM 6 Sheets-Sheet 4 IN V EN TORS EM/L' Mal/ ammo a. GR/EG Aug. 1, 1950 E. LABIN arm. 2,515,885

RELAY SYSTEM Filed April 17, 1944 6 Sheets-Sheet 5 IN V EN TORS A TTOHNEY Patented Aug. 1, 1950 RELAY SYSTEM Emile Labin, New York, and Donald D. Grieg, Forest Hills, N. Y., assignors to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application April 17, 1944, Serial No. 531,353

4 Claims.

This invention relates to radio communicating systems and more particularly to radio multichannel broadcasting and relaying for further broadcasting in the ultra-high frequencies.

In our copending application for Broadcastin Systems, Serial No. 529,932, filed April 7, 1944, we disclose a radio multi-channel broadcasting system wherein the transmitter station is provided with an omni-directional antenna located at an advantage point such as at the top of the highest building of a city or on a tower located at some other high elevation within the area to be served. The transmitter includes means for producing a plurality of channels each represented by a series of pulses interleaved in sequence with a train of pulses belonging to a plurality of series making up the other channels, the train of interleaved pulses being translated to a given carrier frequency which is radiated over the omni-directional antenna. The transmitter includes modulator means for each channel of pulses whereby a plurality of different programs, one for each channel, are broadcast simultaneously over the antenna at one given carrier frequency. The pulses of one of the channels are given an identifying characteristic such as a given width or other signalling characteristic different from the pulse characteristics of the other channels for synchronizing radio receivers to the transmission sequence of the channels. This permits the broadcasting of a plurality of different programs from one high point so that receivers located within the range of the station may be equipped with antennas, directional or otherwise, arranged in alignment with the antenna of the transmitting station. Each receiver thus can obtain optimum reception of all the programs broadcast within that area, the only tuning required being time selection-of the channels with respect to the synchronizing channel, the receiver being, of course, initially adjusted for reception at the common carrier frequency.

It is one of the objects of our present invention to provide a method and means for relaying from one or more broadcasting areas multi-channel carriers or sub-carriers and rebroadcasting the same over another area.

Another object of the invention is to provide a method and means to receive a plurality of chan nels of communication from one or more sources, to suppress those channels not Wanted and to transmit the others on a single carrier.

1 A further object of the invention is to provide a method and means for receiving from a broadcasting station, either direct or by intermediate relays, a carrier, pulse modulated with a plurality of program channels and retransmitting the channels; and at such retransmitting point, as a further object, to provide a method and means to suppress certain channels and/or to add still other channels, as may be desired.

Still another object is to provide a receiver for selectively receiving the channels of a multichannel transmitting medium.

For the sake of clarity, pulses making up a channel will be referred to as a series of pulses, while the interleaved pulses of a plurality of channels will be referred to as a train.

The above and other objects of the invention will become more apparent upon consideration of the following detailed description to be read in connection with the accompanying drawings, in which:

Fig. 1 is a diagrammatic panoramic view of New York city and vicinity illustrating the centralized multi-channel broadcasting principle of our invention;

Fig. 2 is a block diagram of a multi-channel broadcasting system utilizing pulse width as the distinguishing characteristic for the synchronizing channel;

Fig. 3 is a schematic wiring diagram of a phase shifter, time modulator and pulse width shaper for one of the channels of the system of Fig. 2;

Fig. 4 is a graphical illustration used in explaining the operation of the circuit of Fig. 3;

Fig. 5 is a, block diagram of a radio receiver capable of selectively receiving channels transmitted by the system of Fig. 2;

Fig. 6 is a graphical illustration used in explaining the receiving operation of Fig. 5;

Fig. 7 is a block diagram of a relay repeater whereby all of the sub-carriers of the carrier frequency receiver are transmitted over an omnidirectional antenna;

Fig. 8 is a block diagram of a repeater broadcasting station arranged to suppress certain of the channels and in insert other channels;

Fig. 9 is a schematic wiring diagram of a chan nel suppressor that may be used in the circuit of Fig. 8; and

Fig. 10 is a graphical illustration of the operation of the circuit of Figs. 8 and 9.

Referring to the panoramic view of New York city and vicinity shown in Fig. l, the multi-channel broadcasting station is shown located, for illustrative purposes, in the Empire State building In which affords the highest centralized location in the broadcasting antenna 12. The antenna may be of any known omni-directional' type. The building may house several of the studios while other Studios and sources of signals may be located in still other buildings as indicated at 2, 3 and N, each studio being connected by line to the control room of the broadcasting station. By this arrangement a number of programs is supplied for modulation of diiferent carriers or sub-carriers such as series of pulses which, when properly timed, interleave in sequence to form a single train. of pulses to modulate a single transmitter for simultaneous transmission at a common carrier frequenc F1 over antenna l2. Thus each studio, rather than being identified by an individual transmitting frequency, is represented by a train of pulses interleaved in time position with the pulses carrying programs from other studios. Listeners at receiving points such as 2!, 22, 23, 2t and 25 tune their respective receivers by time channels rather than frequency to choose a desired one of the programs transmitted.

In addition to the selective reception, th mu1tichannel transmission may be relayed by repeater broadcasting stations where the receiving antenna thereof is in visual alignment with the transmitter antenna 52 as indicated at 293. If the repeater broadcasting station is beyond range as indicated at 21, relay repeaters such as indicated at 28 and 29 may be located at appropriate .points in-between. The repeater broadcasting systems rebroadcast the channel pulses after amplification either at the same or at different carrier frequency, as the case may require.

In Fig. 2, the separate studios are shown connected by lines to one Or more pulse modulating channels of the system. Studio I, for example, is shown connected through switch 38 to channel 2 which includes a modulator 32 indicated, for example, as P. T. M. (pulse time modulator) coupled to a pulse width shaper d2. Channel I produced by cusper generator 30 and pulse shaper 3! is shown not modulated with a. program since it is best to use the pulses of one channel for synchronizing only. This provides a steady bebloclze ing pulse, as will be made clear hereinafter. The cusper generator til is controlled by a base wave produced by generator 35. The additional pulse modulating channels are also controlled by the base wave from generator 35 but the timing thereof is controlled by individual phase shifters as indicated at 35 for channel 2, the difference in timing with respect to channel 5 being indicated by the symbols ta, ta, etc. The modulation of the pulses of each channel may be controlled by an appropriate switching arrangement as indicated at 3! and 38.

To distinguish for synchronizing purpose the pulses of channel I from the pulses of other channels, the pulse width shaper 3! is arranged to give the pulses of channel i a width difierent from the pulse widths determined by the pulse width shapers 42, 43, etc. This method of identifying the synchronizing pulses is clearly shown by curve 6a of Fig. 6. The pulses of channel l are considerably wider than the pulses of the other channels which, in this case, comprise a given narrow width. The interleaved train of channel pulses produced at the outputs of the shapers H, 42, 43, etc., is applied to a carrier translator 50 for translation to a common carrier frequency to be transmitted over omni-directional antenna l2. The antenna shown is of the type disclosed in U. S. patent to A. Alford, 2,283,897.

Studio 3 is shown in Fig. 2 to be connected to two different channels. This is to indicate that a given studio may have more than one channel for broadcasting purposes. It will also be understood, in this connection, that while in existing broadcasting systems programs are generally transmitted for voice and musical programs, other types of intelligence ma also be transmitted. For example, pulses may be transmitted in this manner as facsimile signals, the pulses being used directly as the facsimile build-up characters. The transmitted pulses may also constitute a sound track for television as well as synchronizing pulses required for controlling the line and frame scanning in facsimile and television transmission. In addition, the two channels may serve for a binaural sound transmission for a single program.

Fig. 3 shows a circuit of a cusper type of P. T. M. modulator 32a such as may be employed in the channels of the system of Fig. 2, together with a phase shifter 36a and a pulse width shaper 42a. The phase shifter 36a comprises a condenser-resistor network CR1R2, the relative values of which determine the phase shift of the base wave applied thereto from base wave generator 35, Fig. 2. Assuming that there is no phase shift of the base wave required as in the case of channel I, then the wave may be regarded as of the phase position indicated by wave ill in curve is, Fig. 4, when applied to primary coil 12 of the coupling transformer 13.

The modulator circuit includes two secondary coils l4 and 15 coupled to the control grids of two vacuum tubes 16 and T! in push-pull arrangement similar to a full-wave rectifier. The modulator amplifies and, in effect, full-wave rectifies the wave H1, curve 4a, Fig. 4, to obtain a cusper wave 8!], curve 4b. Curve 4c shows the cusper wave for channel 2 determined in time position by the phase position 10a, curve 4a, of the base wave.

Time modulation of the cusper wave is produced by applying the signal intelligence over input connection 82 with respect to ground to primary coils 83 and B4 on the transformer 13. While the rectification of these waves ma be symmetrical relative to zero axis 61, it is shown for purposes of illustration as being offset by diiferent biasing potentials B5 and 66. This gives the effect of an offset axis El a about which modulation takes place. The signal intelligence operates, in effect, to vary the wave 10 relative to its ofiset axis 61a as regards the full-wave rectification, This relative variation between the wave and the zero axis thereof is illustrated in curve M by the upper and lower modulation limits 86 and 81. When the input signal varies the relative relation between the offset axis 67a and the wave 10 as indicated by limit 86, the cusper wave 9, for example, is displaced as shown by the broken line 90a, and when varied to the opposite limit 8! it is displaced as shown by broken line 901). It will be observed that the signal wave thus varies the time positions of the cusps 9|, 92, 93 and 94 in push-pull manner toward and away from each other thereby decreasing or increasing the time interval between successive cusps.

For transmission purposes, the cusps are clipped from the wave and, if desired, may be shaped to form substantiall rectangular pulses. A suitable shaper circuit is shown at 42a, Fig. 3, it being understood, however, that other known pulse shapers may be used instead. By providing each channel with a shaper circuit of this char-' acter, the shape of the pulses of each channel maybe controlled.

The shaper 42a may be of any known character capable of clippingbetween two desired levels, but preferably is of the character disclosed in our copending application, Serial No. 437,530, filed April 3, 1942. It comprises a double diode clipping circuit wherein the plates of the two diodes IOI and I02 are connected together and the cathode of tube IN is connected through coupling condenser I03 across the load resistor I04 of the modulator 32a. The cathode of diode IN is connected through a resistor I06 to a potentiometer I01. The plates of the two tubes are connected through a'resistor I08 to a second potentiometer I09. The cathode of the tube I02 is connected through a resistor I I0 to ground,

The two diodes I 0| and I02 operate together as a gate clipper for clipping the cusper wave 80, for example, between limit levels III and H2, curve 4b, the width of the gate being controlled by the adjusting of potentiometer I 01 and the position of the gate relativ to the wave is controlled by adjustment of the potentiometer I09. The'gate position of the clipping levels III and H2 on wave 80, produces a pulse of the width W1, curve 4d. The pulse Ia of curve 4d is shown to be amplified, it being understood that the pulse width shapers may include one or more amplifying stages as indicated at I I5.

For channel 2, the cusper wave 90 is clipped at gate levels H3 and H4 as indicated in curve 40, These different gate levels are effected by adjusting potentiometer I09. This gate clipping results in pulse 211 with width W2 which is less than the width W1. It will thus be clear that by proper adjustment of the shaper circuit, the pulses of any channel such as channel I may be made distinctive from the pulses of the other channels. This distinction in width is shown incurve to, Fig. 6, the wider pulses of channel I being used as synchronizing pulses for the receivers. Broken lines 900 and 90d represent the maximum limits of time modulation of the pulses 2a.

Referring to Fig, 5, we have shown in block diagram a receiver of the character synchronizable to the transmission sequence of the channel pulses by means of the distinction in pulse width between the synchronizing channel and the other channels of the system. The receiver includes a carrier frequency amplifier and detector I whereby the carrier pulses of curve 6a are translated into the video pulse form of curve 6b. The videopulses are applied to a synchronizing channelselector I22 which, in this case, may be a pulsewidth discriminator of any known type.

.If desired, a pulse width discriminator of the character disclosed in our copending application, Serial No. 487,072, filed May 15, 1943, now U. S. Patent No. 2,440,278, granted April 27,1948, may

be employed. This width discriminator includes 1 a resonant circuit which is shock-excitable in response to the leading and trailing edges of the pulses and a damping circuit having a vacuum tube connected across the resonant circuit for damping out the oscillatory energyfollowing one or two undulations, as the case may be. The output from the circuit is provided with a threshold clipper stage which is adjustable to pass energy in response to undulationsproduced from pulses of a width. corresponding to the tuning of the resonant circuit. Should the pulses be of a width different from one-half the period. .of the frese m t which t e semis tunes. the n ul tions thereof will be less than that required to produce conduction in the threshold clipper stage. Thus, pulses varying in width from the desired width are blocked, pulse energy being passed by the clipper stage only in response to undulations produced from pulses of the desired width.

The output pulse energy from the synchronizer channel selector I22 is applied to an adjustable delay device I25 which, preferably, is of a known form of pulse translation type of delay circuit,

whereby the pulse energy may be adjusted in time with reference to the timing of the synchronizing pulses. The retarded pulse energy of the device I25 is applied toa mixer I26 to which isalso applied the video pulse output of the detector I20. It will be understood, of course, that the pulse output of the selector I22 may be shaped to provide a pulse of a width corresponding to the total time space occupied by the pulses of each channel throughout the maximum limits of mod ulation thereof. This output pulse energy It which we call deblocking pulses is shown by curve 60. Retardation of the pulse energy is shown to be an amount is thereby aligning the deblocking pulses It, as shown in broken line,

inal modulated pulses of the selected channel produced at the transmitter, Fig. 2. These output pulses are applied to the control grid of the demodulator tube I 54 and cause tuned circuit I56 connected to the screen grid of the tube to oscillate at a desired frequency producing in the tube I54 a combined grid potential effect in the form of a combination of the wave generated in the circuit I and the incoming pulses from tube I42. The circuit I50 is preferably tuned to some harmonic of the cadence frequency as determined by the period T, curve 61), so that as the pulses are displaced due to modulation signals the output pulses of tube I54 will be raised to dilferent levels depending upon their time displacement. Accordingly, in the output of tube I 54 will appear a modulation envelope of pulses carrying signal modulationsaccording to the amplitude measurements thereof. Low-pass filter I5! removes the pulses of the output envelope which is applied to speaker I60. For a further understanding of the principles of this type of de modulator, reference may be had to the copendmg application of D. D. Grieg, Serial No. 459,959,-

filed September 28, 1942, now U. S. Patent No. 2,416,306, granted February 25, 1947.

A simple form of broadcasting repeater is, 'shown in Fig. 7.

The repeater includes a detector 200 having a directional receiving antenna 2 0I adapted to be aligned with the omni-directional antenna of the main or other broadcasting l station such as station I 0, Fig. 1, or for align- Y ment with antennas of directional relays such as indicated at 28 and 29, Fig. 1. The detector 200 translates the carrier frequency pulses to video, 1

the video pulses being amplified at 204 and translated into a carrier by modulator 205 of a frequency different from the carrier received. This second carrier frequency is then transmitted from an omni-directional antenna 200. Thus, all the channels received are amplified and rebroadcast. -sincethe new carri r, frequency is different f r.om..i:

that received, the area covered by the rebroadcast may overlap somewhat the area covered by the main broadcast, without causing interference. It will be recognized that this form of broadcast repeater is simple in construction and relatively inexpensive. In a network system, broadcast re peaters of this character may be used for thinly populated areas.

For larger populated areas Where it is desirable to produce locally certain of the programs to be broadcast or to add others from other sources, a more complex repeater station along the lines shown in Fig. 8 may be installed. This system also includes a detector 218 for receiving the carrier frequency which is modulated with channel pulses for translation into video form. For synchronizing purposes, the repeater includes a synchronizer channel selector 2l2 which selects the synchronizing pulses from the train of channel pulses received. Curve [Ba of Fig. 10 shows, for example, trains of channel pulses that may be received by the detector. Each train is shown to include six channels in sequence and a gap between the sixth and Nth channels which may include additional channel pulses, not shown, or may represent an unoccupied space in the channel repetition period. Curve lllb rep-resents the synchronizing pulses separated from the pulses of the other channels. These pulses are shown as being of a width greater than the pulses of the other channels and, therefore, may be easily separated therefrom by known forms of pulse Width discriminating circuits or by the form disclosed in our aforesaid copending application, Serial No. 487,072.

The synchronizing pulses are applied to a base wave generator 2M which preferably includes a known form of oscillator adjustable to produce a wave 215 having a frequency corresponding to the repetition rate of the synchronizing pulses. The base wave generator also include a known form of frequency divider whereby the frequency of wave H5 is divided by two thereby producing wave 2I6 which We refer to hereinafter as the base wave since it corresponds in frequency to the base wave produced by the generator 35 at the transmitter, Fig. 2.

For monitoring purposes, the circuit may include one or more channel receivers. One channel receiver is shown to which the base wave 2E6 is applied through phase shifter 220. The base wave is shifted an amount 06 as shown at 2l6a, curve N19, for effecting selective reception, for example, of the pulses of channel 5. The wave energy 2 Mia is applied to a deblocking pulse generator 222 of the clipper-shaper type whereby a deblocking pulse 223 is produced in coincidence with the pulses of channel 6. These deblocking pulses are applied to a mixer 224 to which video pulses from detector 210 are also applied over connection 225. The mixer comprises the usual mixer-shaper circuit having a clipping level 226, curve mg. The deblocking pulses 223 elevate, in effect, the pulse potentials of channel 6 whereby output pulses for channel 6 are produced as indicated by the curve lllh.

The time displacements of the pulses of channel 6 are translated into amplitude displacements by applying the output of mixer 224 to a demodulator mixer 230 to which is applied a demodulating wave from frequency multiplier 228. The base wave 2l6a. is applied to the frequency multiplier where it is increased in frequency according to the adjustment of the multiplier. Curve I02 shows a demodulating wave 229 which is the third harmonic of base wave 2 Mia. It will demodulation purposes.

be understood that the third harmonic isselected only for purposes of illustration and that. in practical operation a'much higher harmonic may be required so as to provide steeper slopes for The pulses of channel 6 are superimposed as grid potential upon the wave 229 thereby producing conduction in the modulator mixer when the potential exceeds clipping level 23L The mixer 230 thus produces a pulse output which varie in amplitude according to the time displacement of the input pulses, This translation is clearly apparent from the showing of curves [Oh and I02. The envelope 233 of the output pulses is obtained by applying the pulse to filter 232, the envelope energy being then applied to speaker 234 for reproduction. From the foregoing description it will be clear that any one of the channels 2 to N may be selectively detected by merely controlling the phase adjustment of the phase shifter 220.

Where the channel period is not completely occupied by channel pulses, additional channels may be inserted into the train of pulses, at the repeater station. These additional channels may be produced locally or received over a radio link or line from a remote source. After the channel period is completely occupied with channels so that no-more channels can be added without altering the width and spacing of the channel pulses, certain channel spacing may be assigned for locally produced programs which are of local interest only. Local program channels received from other localities in such space may be suppressed at the repeater station and other programs locally produced at or near the repeater station inserted in their place. This suppressionand substitution, of course, may be made selective with regard to all channels.

The suppression of unwanted channels is accomplished by applying the base wave produced by generator 2 I 4 through a phase shifter 240 whereby the base wave is shifted a desired amount 01 as indicated by the wave 2 I611, curve I M. This shifted wave is applied to a block pulse generator M2 of the clipper-shaper type whereby blocking pulses 2 .3 are produced of a width sufficient to include in coincidence the pulses of channels 4 3 the grid 254 of tube 252. The anodes of the tubes 251 and 252 are connected together across resistor 256. The cathodes of the two tubes are connected across a resistor 25'! across which the output of the tubes is taken as indicated by connection 260. The connection 260 is provided with a clipper stage 262 for clipping the pulse output at level 263, curve 10d. It will thus be seen from the curve that the pulses of channels 4 and 5 are effectively suppressed leaving the pulses of channels I, 2, 3, 6 and N.

'ulators is taken from the generator 2M through phase shifters 213 and 214 whereby the wave energy is shifted in phase by amounts 02 and 63 thereby providing base waves 215 and 2%, respectively, curve l0e.

plied to the modulators in the same manner as These two waves are apdescribed in connection with the modulator circuit of Fig. 3. This provides two series of pulses timed according to the pulses 4x and 5y of curve lllf. These pulses have the same average recurrence rate as the pulses of the suppressed channels 4 and 5 so that they assume approximately the time position thereof in the train of channel pulses. The pulses of channels 03: and 52/ are, of course, preferably shaped as to width by shapers 280 and 28L respectively.

Should it be desired to add a further channel in a gap in the train of channel pulses such as channel position 7, for example, this may be done by shifting the base Wave from generator 284 by amount 04 at phase shifter 284 for application to modulator 295. The program intelligence Z applied to the modulator 285 may be from another local studio or, as indicated in Fig. 8, it may comprise the audio signals received over detector 282 and antenna 283. The output pulses of modulator 285 are shaped at 288 for application to input connection 299. The substitute and/or additional channels are applied to a coupling amplifier 292 together with the pulses of the channels passed by suppressor 259. The resulting train of pulses is thus applied to translator 294 for translation to the desired carrier frequency for radiation over antenna 295.

From the foregoing description it is clear that the repeater broadcasting station of Fig. 8 provides for the monitoring of the received channels, the suppression of unwanted channels and/or the insertion into the train of channel pulses, other channels either produced locall or received from remote sources. It will be readily recognized that the system is flexible in that the channels to be suppressed are selected by adjustment of pulse shifter 249, as well as by the selected width of the blocking pulse. While only one blocking pulse generator is shown, it will be understood, however, that additional blocking pulse circuits for use with suppressor 250 may be added as desired. It will also be understood that additional local channels may be provided, the timing thereof being synchronized to the synchronizing pulses for insertion in the train of channel pulses as the operator may desire.

While we have described above the principles of our invention in connection with specific apparatus and particular modifications thereof, and referred to trains of pulses as comprising the channel carriers, it will be readily understood that other types of carriers or sub-carriers such as different sub-frequency carriers may also be employed. It is to be clearly understood, therefore, that this description is made only by Way of example and not as a limitation on our invention and the scope of the accompanying claims.

We claim:

1. A radio multichannel broadcasting system, comprising a first transmitter station having a transmitting antenna mounted at a vantage point to transmit energy over a designated area, means for producing a plurality of series of signal pulses. each series constituting a separate signal channel, means for interleaving all of said series of pulses, means for modulating the signal pulses of each channel according to the intelligence to be transmitted through their respective channels, means for modulating a carrier wave of a given frequency with the resultant pulse train, means for feeding the modulated carrier wave to the transmitting antenna for radiation of energy therefrom, a plurality of separate points for producing signals to provide the aforesaid intelligence modulation of the signal pulses; and a second station having a transmitting antenna mounted at a vantage point to transmit energy over a second separate designated area, and hav ing a receiver comprising means for receiving signals of said given carrier frequency over a directive receiving antenna aligned to receive signals from said first mentioned transmitting antenna, means for removing the carrier frequency from said received signals to reproduce the signal pulses, adjustable selecting means for separating the signal pulses of at least one desired channel, means for modulating a carrier wave of a frequency other than said given frequency with the pulses of the separated channel, and means for feeding the last mentioned modulated carrier wave to said second transmitting antenna for radiation of energy therefrom.

2. A broadcasting system according to claim 1, wherein characteristic synchronizing pulses separate the signal pulses into cyclically recurring groups, and means in the adjustable selecting means of the receiver responsive to the synchronizing pulses.

3. A broadcasting system according to claim 1, wherein the second station includes one or more relays located between the first transmitting antenna and the receiving antenna, each of said relay stations having directive transmitting and receiving antennas aligned to provide directive operation between said first mentioned antenna and the receiving antenna of said second station.

4. A broadcasting system according to claim 1, wherein said second station includes means to suppress the pulses of a selected channel from the train of channel pulses received from the first mentioned transmitter station, means to substitute in place of the suppressed pulses the pulses of another channel, and means for modulating said second frequency with the pulses of said other channel in addition to the pulses of the separated channels for rebroadcasting over said second transmitting antenna.

ENIILE LABIN. DONALD D. GRIEG.

REFERENCES CITED The following references are of record in the file of this patent:

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